1. Field of the Invention
This invention relates to a photographing apparatus having so-called image blur compensation means having the function of compensating for the image blur of a photographed image caused by the vibration of a camera such as the vibration of a hand, and particularly to a photographing apparatus having image blur compensation means designed to control the amount of compensation of image blur on the basis of the focal length information and focus distance information of a photographing system, and compensate for image blur highly accurately.
2. Related Background Art
Generally, if a camera is vibrated by the vibration of a hand or the like when photographing is being effected with the camera held in hands, image blur will occur in a photographed image to deteriorate the quality of image. For this reason, there have recently been proposed various photographing apparatuses provided with image blur compensation means designed to compensate for image blur caused by the vibration of a camera such as the vibration of a hand.
FIGS. 7 to 9 of the accompanying drawings are schematic views of the essential portions of the optical system of a photographing apparatus having image blur compensation means proposed by the applicant in Japanese patent Laid-Open No. 1-116619. In these figures, the photographing system is constituted by a magnification changing optical system, and some of the lens units of the magnification changing optical system are eccentrically driven to compensate for image blur caused by vibration or the like.
The magnification changing optical system shown in these figures is a so-called two-unit zoom lens which has in succession from the object side a first lens unit 31 of positive refractive power and a second lens unit 32 of negative refractive power and in which the spacing between the two lens units is changed to effect a magnification change and the first lens unit 31 is moved on the optic axis to effect focusing. The reference numeral 33 designates an imaging surface such as an image pickup surface or film, the reference numeral 35 denotes a light beam imaged at a point A on the imaging surface 33, and the reference numeral 34 designates the optic axis of the magnification changing optical system. FIG. 9A shows the optical arrangement of the wide-end, and FIG. 9B shows the optical arrangement of the telephoto-end.
FIG. 7 is a schematic view of the optical system when there is no vibration of the camera and there is no image blur. In FIG. 7, the light beam 35 is imaged at a point A on the imaging surface 33 at the wide-end and the telephoto-end because there is no vibration of the camera and there is no image blur.
FIG. 8 is a schematic view of the optical system when the vibration of the camera is transmitted to the magnification changing optical system to cause the image to be blurred. In FIG. 8, for simplicity, there is shown the imaged state by the blur of the light beam when on the wide-side and the telephoto-side, the entire magnification changing optical system is forwardly inclined about the point A and the blur of the image is caused.
That is, the light beam 35 which should originally be imaged at the point A is imaged at a point B on the imaging surface 33 on the wide-side and at a point C on the imaging surface 33 on the telephoto-side.
Now, when the film is under exposure and the magnification changing optical system is monotonously inclined from the state shown in FIG. 8A to the state shown in FIG. 8B and the blur of the image is caused, the image which should be formed as a point image at the point A if there is no blur is formed as a blurred line image of a segment AB on the wide-side and a blurred line image of a segment AC on the telephoto-side.
FIGS. 9A and 9B are schematic views when compensation is effected for the blur of the image shown in FIG. 8. In FIG. 9, the first lens unit 31 is used as a movable lens unit for image blur compensation and is made parallel-eccentric in a direction orthogonal to the optic axis 34 to compensate for the blur of the image. In these figures, the reference character 34a designates the optic axis of the first lens unit, which is parallel to the optic axis 34 of the first and second lens units which has been a common axis before the compensation of the blur.
As shown in FIG. 9, the first lens group 31 is made parallel-eccentric by a predetermined amount for the blur of the image caused by the forward inclination of the entire magnification changing optical system, whereby the light beam which would be imaged at the point B at the wide-end and at the point C at the telephoto-end as shown in FIG. 8 can be imaged at the point A which is the original imaging point.
Image stabilization is achieved by the first lens unit being thus made parallel-eccentric. In FIGS. 7 to 9, instead of the first lens unit, the second lens unit can be made parallel-eccentric to compensate for the blur of the image in a similar manner.
Generally, the amount of image blur y.sub.I when the camera is inclined by an angle .theta. by vibration or the like is EQU y.sub.I =f..theta.(1+.beta.), (1)
where f is the focal length of the photo-taking system and .beta. is the then imaging magnification (lateral magnification). When here, the amount of parallel eccentricity of the lens unit for compensating for the amount of image blur is y.sub.L, the degree of sensitiveness S as anti-vibration means is EQU S=y.sub.I /y.sub.L. (2)
As is clear from equations (1) and (2), the degree of sensitiveness S of the anti-vibration means depends on the focal length f and imaging magnification .beta., i.e., the focus distance, of the photo-taking system.
In the magnification changing optical system shown in FIG. 7 to FIG. 9B, during focusing, the first lens unit 31 is moved on the optic axis and therefore, the focal length as the entire magnification changing optical system is variously varied by the focus distance. This holds true not only of the two-unit zoom lens shown in these figures, but also of magnification changing optical systems of other types.
Particularly recently, the so-called rear focus system has often been adopted as a focus system to achieve the compactness of the magnification changing optical system, but the adoption of this rear focus system results in the focal length of the entire system being greatly varied by the focus distance.
In a photo-taking system having the conventional image blur compensation means, the degree of senstiveness which is the eccentric movement of a compensation lens unit for image blur compensation has been set by the use of only the value of the focal length of the photo-taking system. Therefore, where use is made of a photo-taking system whose focal length is greatly varied by the focus distance, the degree of sensitiveness of image blur compensation is greatly varied by the focus distance, and this has led to the problem that image blur cannot be compensated for highly accurately. This has held true not only of the magnification changing optical system, but also of photo-taking systems of single focal length. The technique of varying the amount of compensation movement of a compensation lens by the position of a focusing lens is proposed in U.S. application Ser. No. 627,924.